1. Field of the Invention
The present invention relates to caller identification (CID) technology within a cordless telephone environment. More specifically, it relates to the receipt and display of Type II CID data by multiple cordless telephones within a single household.
2. Description of the Related Art
Cordless telephones have proven to be popular in domestic, business and industrial environments due to the unrestricted freedom of movement they provide users. In fact, in 1997, for the first time ever, sales of cordless telephones exceeded sales of corded telephones with total cordless units sold being in excess of 28 million. Furthermore, total sales for 1998 are expected to have increased over 1997 sales by at least 25 percent.
With a cordless telephone, a telephone subscriber is not confined by the limitation of a station set extension cord. Instead, the subscriber has complete freedom of movement within a radio frequency (RF) link range of up to about 300 m between a stationary base and its cordless portable handset.
Along with the continued growth of cordless telephone sales are the increased umber of conveniences being offered for use on cordless telephones. Among the any such services are caller identification (CID) and call waiting.
CID is a well known feature that allows a telephone user to identify the party making an incoming call before the call is answered. When a telephone call is directed to a customer having the CID service, the central telephone office (CO) transmits a CID message concurrently with the incoming call. Specifically, the CID data is typically transmitted to the recipient between rings of the incoming call. Upon receipt of the CID data, the dialed party may use the CID data to screen his or her incoming calls, keep a journal of incoming calls, monitor for prank calls, or for any other personal or business need.
To enjoy the benefits of conventional CID service, a person typically rents or purchases a special component that receives and displays the CID data. This component may, for example, be a separate box that must be connected in line with a standard telephone unit. Cordless telephone subscribers may take advantage of the CID service by utilizing the special CID box in combination with the cordless base station. Still others, may be in possession of a cordless telephone unit capable of displaying the CID data at the handset itself through an integral CID display. Such units allow both the telephone handset and the CID feature to be mobile, thereby adding to the overall convenience of the telephone.
Call waiting is an equally well known feature, whereby a subscriber is virtually assured that he or she will not miss an incoming telephone call. That is, if the subscriber is currently using the telephone, and another call comes through on the same line, a slight tone will be heard by the subscriber. If the subscriber wishes, the current telephone call may be placed on hold while the subscriber checks to see who is on the other line. This is achieved by momentarily pressing a key on the receiver or by depressing an on-hook button. The subscriber may switch back and forth between calls as often as he or she wishes. Similarly to the CID feature, the call waiting feature has been available on cordless telephones for some time now.
Recently, the above described features of CID and call waiting have been combined to create caller identification on call waiting (CIDCW). CIDCW is often referred to in the art as Type II CID. With Type II CID, instead of simply receiving a slight tone, the subscriber can actually discern who is on the other line when they""re already engaged in a telephone conversation by virtue of the received Type II CID information. The subscriber can then make an informed decision about whether to interrupt the on-line caller.
FIG. 1 depicts a block diagram of the xe2x80x9chandshakingxe2x80x9d required in order to implement the Type II CID feature. First, an initial telephone call between the subscriber 10 and a second party 11 is already in progress. As is known in the art, the call between subscriber 10 and the second party 11 is routed through a central office (CO) 13 via communication links 20 and 21. The subscriber 10 actually receives the call on subscriber line 35 through telephone line 37. Next, a third party 12 seeks to place a telephone call directly to the subscriber 10, however, the third party""s 12 call must first be routed through the CO 13, via communication link 14. Next, the CO 13 sends two signals 15 (a subscriber alerting signal (SAS) and a CPE alerting signal (CAS)) to the subscriber 10, alerting the subscriber of the incoming telephone call from the third party 12. The subscriber""s 10 telephone unit then sends an acknowledgement signal 16 back to the CO 13, alerting the CO that it is ready to accept the Type II CID data 17. The CO then sends the data 17 to the subscriber 10, where it is displayed and whereby the subscriber may make an informed decision as to whether the call between him or herself 10 and the second party 11 should be interrupted in favor of the call from third party 12.
Turning now to FIG. 2, a flowchart depicts, in more detail, the above described handshaking between the CO 13 and the subscriber""s 10 telephone unit. Similar to FIG. 1, the process begins with a telephone call being placed from a third party 12 to the subscriber""s telephone at step S1; the subscriber""s telephone unit being well known in the art as customer premise equipment (CPE). Next, the CO 13 directly receives the call from the third party at step S2. Next, the CO 13 determines whether the called CPE 10 is currently in use at step S3. If the CO 13 determines that the CPE 10 is not in use, the call is forwarded directly to the CPE 10 at step S4. However, if the CO 13 determines that the called CPE 10 is currently in use, a subscriber alerting signal (SAS), and a CPE alerting signal (CAS) are sent to the CPE 10 at step S5. The SAS is a low frequency tone (e.g., 440 Hz), audible to the subscriber only. The SAS lasts for approximately 300 ms and serves to alert the subscriber of the incoming telephone call. The CAS is a dual-tone signal combination, both being of fairly high frequency (e.g., 2130 Hz and 2750 Hz, respectively) and lasting for approximately 80 ms, or long enough to alert the CPE of the incoming telephone call. Additionally, the CO 13 temporarily removes the second party 11 from the current call during the transmission of the SAS and CAS. Next, the CPE 10 actually receives the signal pair (i.e., the SAS and CAS) 15 at step S6.
The CPE 10 must now decide whether it is prepared to receive the CID data. In so deciding, the CPE 10 determines whether any additional extensions on the same telephone line are currently in use (i.e., in addition to the CPE) at step S7. Most CPE manufacturers detect whether other extension(s) are off-hook by monitoring the line voltage. If the line voltage drops below a certain value, the CPE assumes there is another extension off-hook. If there is another device (or devices) in use, they all receive the SAS/CAS signal pair 15 concurrently with the CPE. The CPE 10, however, cannot at that time accept the CID data because all off-hook units, including all extensions, must be muted in order to receive the CID data and as the state of the art currently exists, the CPE 10 is incapable of muting other off-hook units. Therefore, the CPE 10 will continuously check to see if the other extensions have been deactivated (i.e., placed back on-hook), so as to enable the receipt of CID data by all CID-capable telephones coupled to a common telephone line.
If the CPE 10 is the only telephone currently off-hook, the CPE 10 will then mute the CPE handset at step S8 in preparation for sending acknowledgment signals back to the CO 13, thereby alerting the CO 13 that it is prepared to receive the CID data 17. The acknowledgement signals are sent to the CO 13 at step S9 in dual tone multi frequency (DTMF) format (i.e., xe2x80x9ctouch tonexe2x80x9d). Upon receipt of the DTMF acknowledgement signal 16 at step S10, the CO 13, in turn, forwards the CID data 17 to the CPE 10 at step S11, whereby the subscriber may then make an informed decision as to whether the call that is already in progress should be interrupted in favor of the incoming call from the third party.
From the description above, it should be readily apparent that an important inquiry focuses on whether another extension is concurrently being used within the same household, and on the same telephone line, as the CPE 10. This is relevant because, as described at steps S7 and S8 of the FIG. 2 flowchart, not only must the handset of the CPE be muted before it""s able to receive the CID data 17 from the CO 13, but all other off-hook extensions must be on-hook since the CPE 10 is currently incapable of muting any such off-hook extensions.
The reason for muting the CPE handset is two-fold: i) muting the CPE handset prevents the subscriber from hearing the DTMF acknowledgement signal, the signal being of considerable magnitude and is likely to be somewhat disturbing to the listener; and ii) muting the CPE handset prevents interference from speech and other noise from being transmitted along with the DTMF acknowledgement signal.
Furthermore, if more than one unit is off-hook, each of the off-hook units will seek to be the unit that issues the DTMF acknowledgment signal; a scenario likely to result in confusion and system malfunctions.
Since the CPE is currently incapable of muting any off-hook extensions it has detected, no cordless telephones that are coupled to a common telephone line can receive CID data although they are intended to incorporate the CID feature. Thus, there exists a need for an apparatus and system which allows for multiple off-hook cordless telephones that are connected to a common telephone line to receive Type II CID data.
The present invention overcomes the problems associated with the prior art and provides a method and system for receiving Type II CID data in an environment containing multiple off-hook cordless telephones, all being fitted for receiving CID data, and all being coupled to a common subscriber line. This is achieved by coordinating the sending, receiving, and acknowledging (i.e., handshaking) of control signals between the multiple cordless telephones and the CO. In a preferred embodiment of the invention, the communication between cordless telephones takes place through a wireless connection between each off-hook slave extension and a master unit.
In accordance with the present invention, the handshaking results in the sending of a muting command signal to each off-hook extension and also the sending of a DTMF acknowledgement signal by the CPE to the CO acknowledging the preparedness of the multiple cordless telephones for receiving CID data. Thereafter, the CID data is actually sent to the subscriber line.
The above described process allows a telephone subscriber to have multiple cordless telephones coupled to a common telephone line and, wherein each of the cordless telephones receives CID data. That is, e.g., a CID fitted cordless telephone may be placed in all rooms of the home without requiring additional wiring or a special connection to the existing telephone line. Furthermore, the invention may be incorporated into any telephone that uses a wireless link to pass speech information between its handset and its base station.